Originally, an interrogative pronoun, later, a relative pronoun also; -- used always substantively, and either as singular or plural. See the Note under What, pron., 1. As interrogative pronouns, who and whom ask the question: What or which person or persons? Who and whom, as relative pronouns (in the sense of that), are properly used of persons (corresponding to which, as applied to things), but are sometimes, less properly and now rarely, used of animals, plants, etc. Who and whom, as compound relatives, are also used especially of persons, meaning the person that; the persons that; the one that; whosoever.

"Let who will be President."

Macaulay.

[He] should not tell whose children they were.
Chaucer.

There thou tell'st of kings, and who aspire;
Who fall, who rise, who triumph, who do moan.
Daniel.

Adders who with cloven tongues
Do hiss into madness.
Shak.

Whom I could pity thus forlorn.
Milton.

How hard is our fate, who serve in the state.
Addison.

Who cheapens life, abates the fear of death.
Young.

The brace of large greyhounds, who were the companions of his sports.
Sir W. Scott.

2.

One; any; one.

[Obs., except in the archaic phrase, as who should say.]

As who should say, it were a very dangerous matter if a man in any point should be found wiser than his forefathers were.
Robynson (More's Utopia).